1. Technical Field
The present disclosure relates to cooling of electric motors.
2. Background Art
To obtain good performance and long life of an electric motor, cooling is essential. In some motors, a fluid is sprayed onto winding ends of the coil to provide a higher heat transfer rate than possible with forced air convection. It is important to attempt to uniformly spray the end windings. In one example shown, oil is sprayed from the center, i.e., from a center-mounted rotor that has an oil supply, toward the windings. A temperature differential between the inner side of the end windings and an outer side of the end windings limits the maximum performance and causes differential expansion and stresses thereby limiting the life of the motor. In one alternative, a heat sink is placed over the ends of the end windings to even out the temperature variation. However, the outer surface of the end windings is variable and highly convoluted as it is made of many wires placed next to each other. Thus, it is very difficult to obtain good contact between the heat sink and the windings and the overall heat transfer is much less than directly spraying the inner side of the end of the windings. The heat transfer rate between two surfaces can vary by orders of magnitude if even a slight air gap exists between the two. It is known to pot the windings in epoxy to obtain good contact. However, even epoxy that includes solids to enhance heat transfer may fail to be sufficiently thermally conductive.